According to Goldman Sachs search is the most
interesting of the three options. Facebook already has some elementary search
capabilities but it has yet to be developed very cohesively.

And Zuckerberg's comments last week clearly show that
the company is planning to monetise this aspect of its activity.

An external ad network is also inevitable. Google is
the established leader in the segment and it had built up a humongous base with
its Cost per Click (CPC) strategy.

While Google has the first mover advantage and has
fined tuned its technology in this area for years, Facebook has the advantage
of having a big traffic "that an external ad network might increase their
revenues by 2x or more."

In April this year a blog on Web Pro News had pointed
out that Facebook's CPCs had risen 28 percent in the first quarter while that
of Google had actually seen a decline of 12 percent in the same period. This
was at a time when Facebook had still not gone public and its financials were
still hidden.

Considering the kind of information that is available
with Facebook in terms of personal particulars of its users and Ad Sense kind
of a product seems to be the most likely way for it to go.